WW2 is raging in the skies over England. But for Kember and Hayes there is murder underground. January 1941. The Luftwaffe continues its assault on Britain from the sky, but ATA pilot Lizzie Hayes is grounded after a crash. Itching to be of use, she hears that DI Kember is investigating the death of a coal miner in Kent and sees her chance to help. They discover the miner died from carbon monoxide poisoning but Kember instinctively suspects foul play. Was it an accident, or murder? Armed with her forensic psychology skills, Lizzie helps Kember interview the other miners, and it soon becomes apparent that nearly everyone had a motive for murder. Despite heavy snowfall threatening to cut off the mine, Kember and Hayes are certain the best clues will be found in the depths of the pit itself, and demand that the men-all suspects-lower them into the dark tunnels... When the power goes out and they find themselves trapped, they must confront not only their blossoming feelings for each other but also the prospect that they may never see daylight again. And, even if they do, will they be any closer to finding the killer?